ExceptionChainingTest uses a function to raise an arbitrary exception. Problem: the function and its parameter becomes part of the exception traceback. Shortly, the exception links indirectly to itself in a nice reference cycle...

Example:
---
import traceback

class Err(Exception):
    def __del__(self):
        print("del")

def raise_exc(exc):
    raise exc

e = Err()
try:
    raise_exc(e)
except Exception as e:
    t = e.__traceback__
#traceback.clear_frames(t)
e = None
print("exit")
---

Uncommand the call the clear_frames() to see the exception deleted before the exit.